With the increased use of higher pressures and temperatures and many different fluids, many of which contain foreign substances, corrosives and other contaminants, and practically all requiring flow control, much consideration has been given to the matter of sealing and flow controlling devices. In most cases, the devices are valves of various types. Cost of manufacture, tight manufacturing tolerances, ease of installation and operation, reliability, minimization of damage by contaminants and replacement of seals are factors to be considered. A major one is the availability of a bubble-tight reliable seal which utilizes the pressure of the fluid being controlled to enhance the sealing in the closed position of the valve.
One use of the invention is in butterfly valves and the present invention will be described in conjunction therewith.